P0677 code meaning
Cylinder 7 Glow Plug Circuit/Open
Powertrain system Generic code P06xx codes Check engine light
What P0677 means
Modern diesel glow systems switch each glow plug through its own power semiconductor (in a glow plug module or the engine module), so current and faults can be measured per plug. CARB requires glow plugs to be checked for current and voltage drop and, since model year 2010, a single faulty plug to be detected and named. P0677 means the load circuit of the cylinder 7 glow plug is open while glowing. Thresholds: GM engine-module drivers 200 kΩ or more (10 of 20 samples, two trips), GM's L5P glow module less than 4.0 A, Ford's 2023 6.7 L Power Stroke less than 1 A (cylinders 7 and 8 exist only on the V8). Older GM systems (LB7, LML) report open and short under this code. GM fixed false glow plug codes on 2017–20 heavy-duty diesels by reprogramming the glow module.
P0677 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0677
- Check engine light (GM also glow plug lamp)
- Harder cold start in low temperatures
- Rough idle and white smoke after a cold start
- Often no symptoms when warm
Common causes of P0677
- Most likelyGlow plug cylinder 7 burnt out (element open)
- PossiblePlug connector loose or corroded, terminal nut loose, wire broken
- PossibleGlow module supply or ground (several cylinder codes at once)
- Less likelyGlow module or driver faulty, or software (GM bulletins)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Glow plugGlow plug wiringGlow plug control module
What each part of P0677 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 77 | The exact fault in that area. |
What to do next
- Note P0677 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0677
What does P0677 mean?
P0677 means "Cylinder 7 Glow Plug Circuit/Open". Modern diesel glow systems switch each glow plug through its own power semiconductor (in a glow plug module or the engine module), so current and faults can be measured per plug. It is a generic code, so it means the same on every make.
Is it safe to drive with P0677?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0677 fail an emissions test?
Yes, it can. P0677 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0677 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0677 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.